Allografts of autonomic ganglion transplanted to the intact developing brain can survive for at least 14 months. Normal appearing ganglion cells, neurites and synaptic contacts, initially numerous, gradually diminished over time. Schwann cell processes which surrounded neurites and growth cones and myelinated many larger axons became replete with filaments and formed gap junctions. The Schwann cells had become astrocyte-like. The SCG on the developing cerebellar cortical surface caused the arrest and anomalous migration of the multipotential external granule cells (EGL). Bridges of intact cerebellar tissue, some as long as 1 mm in length, invaded the graft. Neurons and synaptic beds within the bridge implied that EGL cell can differentiate in a foreign environment. Suprisingly, mossy fiber afferents from the spinal cord also entered the graft alongside misplaced granule cells. Other tissues, such as muscle, gland, and nerve transplanted to the developing cerebellar surface indicated heterotopia is caused infrequently. Similarly transplanted non-biological materials caused inflammation and mechanical deformation but did not alter cerebellar development. Thus, certain "tactic factors" in regenerating nervous tissue could influence brain development.